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Message-ID: <CAEf4BzY5oowUpq2x3Uz+TNi=8GJgc1FDzS-u5UqZwNXvkWtSEw@mail.gmail.com>
Date: Fri, 19 Sep 2025 15:22:41 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: "D. Wythe" <alibuda@...ux.alibaba.com>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
martin.lau@...ux.dev, pabeni@...hat.com, song@...nel.org, sdf@...gle.com,
haoluo@...gle.com, yhs@...com, edumazet@...gle.com, john.fastabend@...il.com,
kpsingh@...nel.org, jolsa@...nel.org, mjambigi@...ux.ibm.com,
wenjia@...ux.ibm.com, wintera@...ux.ibm.com, dust.li@...ux.alibaba.com,
tonylu@...ux.alibaba.com, guwen@...ux.alibaba.com, bpf@...r.kernel.org,
davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
sidraya@...ux.ibm.com, jaka@...ux.ibm.com
Subject: Re: [PATCH bpf-next v2 3/4] libbpf: fix error when st-prefix_ops and
ops from differ btf
On Thu, Sep 18, 2025 at 1:03 AM D. Wythe <alibuda@...ux.alibaba.com> wrote:
>
> When a struct_ops named xxx_ops was registered by a module, and
> it will be used in both built-in modules and the module itself,
> so that the btf_type of xxx_ops will be present in btf_vmlinux
> instead of in btf_mod, which means that the btf_type of
> bpf_struct_ops_xxx_ops and xxx_ops will not be in the same btf.
>
> Here are four possible case:
>
> +--------+---------------+-------------+---------------------------------+
> | | st_ops_xxx_ops| xxx_ops | |
> +--------+---------------+-------------+---------------------------------+
> | case 0 | btf_vmlinux | bft_vmlinux | be used and reg only in vmlinux |
> +--------+---------------+-------------+---------------------------------+
> | case 1 | btf_vmlinux | bpf_mod | INVALID |
> +--------+---------------+-------------+---------------------------------+
> | case 2 | btf_mod | btf_vmlinux | reg in mod but be used both in |
> | | | | vmlinux and mod. |
> +--------+---------------+-------------+---------------------------------+
> | case 3 | btf_mod | btf_mod | be used and reg only in mod |
> +--------+---------------+-------------+---------------------------------+
>
> At present, cases 0, 1, and 3 can be correctly identified, because
> st_ops_xxx_ops is searched from the same btf with xxx_ops. In order to
> handle case 2 correctly without affecting other cases, we cannot simply
> change the search method for st_ops_xxx_ops from find_btf_by_prefix_kind()
> to find_ksym_btf_id(), because in this way, case 1 will not be
> recognized anymore.
>
> To address the issue, we always look for st_ops_xxx_ops first,
> figure out the btf, and then look for xxx_ops with the very btf to avoid
What's "very btf"? Commit message would benefit from a little bit of
proof-reading, if you can. It's a bit hard to follow, even if it's
more or less clear at the end what problem you are trying to solve.
Also, I'd suggest to send this fix as a separate patch and not block
it on the overall patch set, which probably will take longer. This fix
is independent, so we can land it much faster.
> such issue.
>
> Fixes: 590a00888250 ("bpf: libbpf: Add STRUCT_OPS support")
> Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com>
> Acked-by: Andrii Nakryiko <andrii@...nel.org>
> ---
> tools/lib/bpf/libbpf.c | 37 ++++++++++++++++++-------------------
> 1 file changed, 18 insertions(+), 19 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index fe4fc5438678..50ca13833511 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -1013,35 +1013,34 @@ find_struct_ops_kern_types(struct bpf_object *obj, const char *tname_raw,
> const struct btf_member *kern_data_member;
> struct btf *btf = NULL;
> __s32 kern_vtype_id, kern_type_id;
> - char tname[256];
> + char tname[256], stname[256];
> __u32 i;
>
> snprintf(tname, sizeof(tname), "%.*s",
> (int)bpf_core_essential_name_len(tname_raw), tname_raw);
>
> - kern_type_id = find_ksym_btf_id(obj, tname, BTF_KIND_STRUCT,
> - &btf, mod_btf);
> - if (kern_type_id < 0) {
> - pr_warn("struct_ops init_kern: struct %s is not found in kernel BTF\n",
> - tname);
> - return kern_type_id;
> - }
> - kern_type = btf__type_by_id(btf, kern_type_id);
> + snprintf(stname, sizeof(stname), "%s%.*s", STRUCT_OPS_VALUE_PREFIX,
> + (int)strlen(tname), tname);
>
> - /* Find the corresponding "map_value" type that will be used
> - * in map_update(BPF_MAP_TYPE_STRUCT_OPS). For example,
> - * find "struct bpf_struct_ops_tcp_congestion_ops" from the
> - * btf_vmlinux.
> + /* Look for the corresponding "map_value" type that will be used
> + * in map_update(BPF_MAP_TYPE_STRUCT_OPS) first, figure out the btf
> + * and the mod_btf.
> + * For example, find "struct bpf_struct_ops_tcp_congestion_ops".
> */
> - kern_vtype_id = find_btf_by_prefix_kind(btf, STRUCT_OPS_VALUE_PREFIX,
> - tname, BTF_KIND_STRUCT);
> + kern_vtype_id = find_ksym_btf_id(obj, stname, BTF_KIND_STRUCT, &btf, mod_btf);
> if (kern_vtype_id < 0) {
> - pr_warn("struct_ops init_kern: struct %s%s is not found in kernel BTF\n",
> - STRUCT_OPS_VALUE_PREFIX, tname);
> + pr_warn("struct_ops init_kern: struct %s is not found in kernel BTF\n", stname);
> return kern_vtype_id;
> }
> kern_vtype = btf__type_by_id(btf, kern_vtype_id);
>
> + kern_type_id = btf__find_by_name_kind(btf, tname, BTF_KIND_STRUCT);
> + if (kern_type_id < 0) {
> + pr_warn("struct_ops init_kern: struct %s is not found in kernel BTF\n", tname);
> + return kern_type_id;
> + }
> + kern_type = btf__type_by_id(btf, kern_type_id);
> +
> /* Find "struct tcp_congestion_ops" from
> * struct bpf_struct_ops_tcp_congestion_ops {
> * [ ... ]
> @@ -1054,8 +1053,8 @@ find_struct_ops_kern_types(struct bpf_object *obj, const char *tname_raw,
> break;
> }
> if (i == btf_vlen(kern_vtype)) {
> - pr_warn("struct_ops init_kern: struct %s data is not found in struct %s%s\n",
> - tname, STRUCT_OPS_VALUE_PREFIX, tname);
> + pr_warn("struct_ops init_kern: struct %s data is not found in struct %s\n",
> + tname, stname);
> return -EINVAL;
> }
>
> --
> 2.45.0
>
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